Method and apparatus for acknowledging a reception of a data packet in a CDMA communication system

ABSTRACT

In a communication system ( 100 ), a method and an accompanying apparatus provide for acknowledging reception of a packet of data. A receiver ( 400 ) at a serving base station ( 101 ) receives a message on an acknowledgement channel ( 340 ) for indicating the reception of the packet of data at a mobile station ( 102 ), and may determine an erasure of the message. A non-serving base station ( 160 ) may also receive the message on the acknowledgement channel ( 340 ) from the mobile station ( 102 ), determines a value of the message, and communicates the value of the message to the serving base station ( 101 ). The serving base station ( 101 ) changes the erasure to the value of the message, and terminates a transmission of a remainder of data units of the packet of data to the mobile station ( 102 ) when the value of the message is a positive acknowledgement from the non-serving base station ( 160 ).

CLAIM OF PRIORITY 35 U.S.C. §120

The present Application for Patent is a Continuation and claims priorityto patent application Ser. No. 09/943,284 entitled “METHOD AND APPARATUSFOR ACKNOWLEDGING A RECEPTION OF A DATA PACKET IN A CDMA COMMUNICATIONSYSTEM”, filed Aug. 30, 2001, granted Aug. 23, 2005 as U.S. Pat. No.6,934,264, and patent application Ser. No. 11/207,467 entitled “METHODAND APPARATUS FOR ACKNOWLEDGING A RECEPTION OF A DATA PACKET IN A CDMACOMMUNICATION SYSTEM”, filed Aug. 19, 2005, which is commonly assigned,and fully incorporated herein by reference for all purposes.

BACKGROUND

1. Field

The present invention relates generally to the field of communications,and more particularly, to communications in a cellular communicationsystem.

2. Background

In code division multiple access (CDMA) communication systems,unnecessary and excessive transmission by a user may cause interferencefor other users in addition to reducing the system capacity. Thecommunication system may provide communication services that includewireless radio transmission of digitized speech, still or moving images,text messages and other types of data. An encoder in a transmitter ofthe communication system may receiver a packet of data for encoding. Theencoding operation produces more data symbols than received. The encodeddata may be divided into several data units. Each data unit may betransmitted in a time slot. Since the data packet is encoded, it ispossible to decode the entire data packet from one or more data unitswithout actually receiving all the data units. After receiving each dataunit, the receiving destination may make a positive or negativeacknowledgement of decoding the entire data packet. If the entire datapacket is decoded successfully before actually receiving all the dataunits associated with the data packet, the transmitter should receive apositive acknowledgment to stop transmitting the remainder of the dataunits. Since the data packet is already properly decoded at thereceiver, the communication resources are wasted if the remainder numberof the data unites are transmitted.

To this end as well as others, there is a need for a method andapparatus for acknowledging reception of a data packet in acommunication system.

SUMMARY

In a code division multiple access communication system, a method and anaccompanying apparatus provide for acknowledging reception of a packetof data. A receiver at a serving base station receives a message on anacknowledgement channel for indicating the reception of the packet ofdata at a mobile station. The receiver at the serving base station maydetermine an erasure of the message. A receiver at a non-serving basestation may also receive the message on the acknowledgement channel fromthe same mobile station. The receiver at the non-serving base stationmay determine a value of the message. The non-serving base stationcommunicates the value of the message to the serving base station. Theserving base station may change the erasure to the value of the messagecommunicated from the non-serving base station. The change may takeplace when the non-serving base station has a better link quality withthe mobile station. The link quality may be determined based on thereceived condition of a pilot channel transmitted from the mobilestation. The non-serving base station may have a better reverse linkquality with the mobile station than the serving base station. When thecommunicated value is a positive acknowledgment, the serving basestation terminates the transmission of the remainder number of dataunits of the packet of data to the mobile station after receiving thepositive acknowledgment from the non-serving base station.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 illustrates a communication system 100 capable of operating inaccordance with various embodiments of the invention;

FIG. 2 illustrates an exemplary forward link channel structure;

FIG. 3 illustrates an exemplary reverse link channel structure;

FIG. 4 illustrates a communication system receiver, for operation in amobile station and a base station, capable of operating in accordancewith various embodiments of the invention;

FIG. 5 illustrate comparison of modulation symbol energy to positive andnegative voltage thresholds and an erasure region; and

FIG. 6 illustrates a flow chart outlining an exemplary flow of steps forimplementing various aspects of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Various embodiments of the invention may be incorporated in a system forwireless communications in accordance with the code division multipleaccess (CDMA) technique which has been disclosed and described invarious standards published by the Telecommunication IndustryAssociation (TIA), Third Generation Partnership Project (3GPP) and ThirdGeneration Partnership Project 2 (3GPP2). Such standards include theTIA/EIA-95 standard, TIA/EIA-IS-856 standard, IMT-2000 standards(including cdma2000 standards and WCDMA standards), all incorporated byreference herein. A system for communication of data as detailed in the“TIA/EIA/IS-856 cdma2000 High Rate Packet Data Air InterfaceSpecification,” incorporated by reference herein, may be moreparticularly capable of incorporating various embodiments of theinvention. A copy of the cdma2000 standards may be publicly obtained,such as by writing to TIA, Standards and Technology Department, 2500Wilson Boulevard, Arlington, Va. 22201, United States of America. Thestandard generally identified as WCDMA standard, incorporated byreference herein, may be obtained by contacting 3GPP Support Office, 650Route des Lucioles-Sophia Antipolis, Valbonne-France.

Generally stated, a novel and improved method and an accompanyingapparatus provide for acknowledging reception of a data packet in a CDMAcommunication system. One or more exemplary embodiments described hereinare set forth in the context of a digital wireless data communicationsystem. While use within this context is advantageous, differentembodiments of the invention may be incorporated in differentenvironments or configurations. In general, the various systemsdescribed herein may be formed using software-controlled processors,integrated circuits, or discrete logic. The data, instructions,commands, information, signals, symbols, and chips that may bereferenced throughout the application are advantageously represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or a combination thereof. In addition, theblocks shown in each block diagram may represent hardware or methodsteps.

FIG. 1 illustrates a general block diagram of a communication system 100capable of operating in accordance with any of the code divisionmultiple access (CDMA) communication system standards whileincorporating various embodiments of the invention. Communication system100 may be for communications of voice, data or both. Generally,communication system 100 includes a base station 101 that providescommunication links between a number of mobile stations, such as mobilestations 102-104, and between the mobile stations 102-104 and a publicswitch telephone and data network 105. The mobile stations in FIG. 1 maybe referred to as data access terminals and the base station as dataaccess network without departing from the main scope and variousadvantages of the invention. Base station 101 may include a number ofcomponents, such as a base station controller and a radio frequencytransceiver. For simplicity, such components are not shown. Base station101 may also be in communication with other base stations, for examplebase station 160. A base station controller and a mobile switchingcenter (not shown) may control various operating aspects of thecommunication system 100 and in relation to a back-haul 199 betweennetwork 105 and base stations 101 and 160.

Base station 101 communicates with each mobile station that is in itscoverage area via a forward link signal transmitted from base station101. The forward link signals targeted for mobile stations 102-104 maybe summed to form a forward link signal 106. Each of the mobile stations102-104 receiving forward link signal 106 decodes the forward linksignal 106 to extract the information that is targeted for its user.Base station 160 may also communicate with mobile stations that are inits coverage area via a forward link signal transmitted from basestation 160. Mobile stations 102-104 communicate with base stations 101and 160 via corresponding reverse links. Each reverse link is maintainedby a reverse link signal, such as reverse link signals 107-109 forrespectively mobile stations 102-104.

In a soft handoff situation, base stations 101 and 160 may becommunicating to a common mobile station. For example, mobile station102 may be in close proximity of base stations 101 and 160, which canmaintain communications with both base stations 101 and 160. On theforward link, base station 101 transmits on forward link signal 106, andbase station 160 on the forward link signal 161. On the reverse link,mobile station 102 transmits on reverse link signal 107 to be receivedby both base stations 101 and 160. For transmitting a data packet tomobile station 102 in soft handoff, one of the base stations is selectedto be a serving base station. The non-serving base station does nottransmit the data packet on the forward link. On the reverse link, bothbase stations 101 and 160 may attempt to decode the traffic datatransmission from the mobile station 102. The information on a reverselink acknowledgment channel may be decoded, in a typical implementation,only by the serving base station that is transmitting the data packet tothe mobile station 102 on the forward link. The non-serving base stationmay ignore the acknowledgment channel.

The turnaround time for decoding the acknowledgment channel and decidingwhether to continue the transmission of the remainder data units isnecessary to be sufficiently short for the serving base station toterminate or continue the transmission of the remainder of data units.Therefore, in a typical implementation, only the serving base stationmay decode and process the acknowledgment channel. If the serving basestation, however, erroneously decodes the acknowledgment channel, thecommunication resources may not be used very efficiently. For example,if a positive acknowledgment (ACK) is erroneously decoded as a negativeacknowledgment (NAK), the transmitter continues to transmit theremaining data units. The transmission continues until the end of thedata packet because the mobile station will not send an ACK messageagain. Continuing the transmission of the remaining data units isunnecessary and wasteful in this case. The communication resources thatare used for the transmission may be used for transmitting other datapackets. Moreover, the transmission may cause unnecessary interferenceto other users. In another example, if a negative acknowledgement (NAK)is erroneously decoded as a positive acknowledgement (ACK), thetransmitter may stop transmitting remaining data units. The receivingdestination therefore does not receive the data packet successfully. Aretransmission of the entire data packet at a later time may benecessary. In this case, the receiver may experience a substantial delayin receiving the data packet, in addition to other problems.

FIG. 2 illustrates a forward channel structure 200 in accordance with anembodiment that may be used for communication on the forward link.Forward channel structure 200 may include a pilot channel 201, a mediumaccess control (MAC) channel 202, a traffic channel 203 and a controlchannel 204. The MAC channel 202 may include a reverse activity channel206 and a reverse power control channel 207. Reverse activity channel206 is used to indicate the activity level on the reverse link. Reversepower control channel 207 is used to control the power at which a mobilestation can transmit on the reverse link.

FIG. 3 illustrates, in accordance with an embodiment, a reverse channelstructure 300 that may be used for communication on the reverse link.Reverse channel structure 300 includes an access channel 350 and atraffic channel 301. Access channel 350 includes a pilot channel 351 anda data channel 353. Traffic channel 301 includes a pilot channel 304, aMAC channel 303, an acknowledgment (ACK) channel 340 and a data channel302. The MAC channel 303 includes a reverse link data rate indicatorchannel 306 and a data rate control channel (DRC) 305. Reverse rateindicator channel 306 is used for indicating the rate at which a mobilestation is currently transmitting. Data rate control channel 305indicates a data rate that a mobile station is capable of receiving onthe forward link. ACK channel 340 is used for communicating whether adata packet has been decoded successfully at a mobile station.

FIG. 4 illustrates a block diagram of a receiver 400 used for processingand demodulating the received CDMA signal. Receiver 400 may be used fordecoding the information on reverse and forward links signals. Received(Rx) samples may be stored in RAM 404. Receive samples are generated bya radio frequency/intermediate frequency (RF/IF) system 490 and anantenna system 492. Antenna system 492 receives an RF signal, and passesthe RF signal to RF/IF system 490. RF/IF system 490 may be anyconventional RF/IF receiver. The received RF signals are filtered,down-converted and digitized to form RX samples at base bandfrequencies. The samples are supplied to a demultiplexer (demux) 402.The output of demux 402 is supplied to a searcher unit 406 and fingerelements 408. A control unit 410 is coupled thereto. A combiner 412couples a decoder 414 to finger elements 408. Control unit 410 may be amicroprocessor controlled by software, and may be located on the sameintegrated circuit or on a separate integrated circuit. The decodingfunction in decoder 414 may be in accordance with the Viterbi algorithmor iterative (turbo) decoding algorithm.

During operation, received samples are supplied to demux 402. Demux 402supplies the samples to searcher unit 206 and finger elements 408.Control unit 410 configures finger elements 408 to perform demodulationof the received signal at different time offsets based on search resultsfrom searcher unit 406. The results of the demodulation are combined andpassed to decoder 414. Decoder 414 decodes the data and outputs thedecoded data. Despreading of the channels is performed by multiplyingthe received samples with the complex conjugate of the PN sequence andassigned Walsh function at a single timing hypothesis and digitallyfiltering the resulting samples, often with an integrate and dumpaccumulator circuit (not shown). Such a technique is commonly known inthe art.

ACK channel 340 is transmitted by a mobile station. Transmission on ACKchannel 340 may be either a negative acknowledgment (NAK) or a positiveacknowledgement (ACK). To limit transmission of ACK/NAK messages on thereverse link by mobile stations in connected state, each mobile stationmay be required to receive an assigned preamble before transmittingACK/NAK messages. Transmission on ACK channel 340 depends on whether themobile station has decoded a matching preamble in a received data packetin receiver 400. Control system 410 may match a decoded preamble to apreamble assigned to the mobile station. After a matching preamble isdetected by control system 410, transmission on ACK channel 340 isallowed in response to each data unit of that data packet until eitherthe packet is successfully decoded or the transmission of the datapacket is completed, whichever comes earlier.

A packet of data may be divided into several data units. Each data unitis transmitted during a time slot. The first one and/or subsequent dataunits may contain a preamble. The mobile station should first detect andmatch the preamble before deciding whether to decode the data. Dataunits subsequent to the first data unit may or may not have thepreamble. After receiving the preamble, the mobile station may transmitNAK messages in response to each data unit of that data packet until atime that the data packet targeted for its user has been decodedproperly or the transmission of the data packet is completed. Therefore,the mobile station sends a NAK message to the serving base station untilthe data packet is decoded. The data packet may be decoded before allthe data units associated with the data packet are completely received.If a received packet of data is correctly decoded, the mobile stationsends an ACK message to the serving base station. The IS-856 standarddescribes and shows an exemplary timing relationship between the timeslots used for transmission of the data units and the time slots usedfor transmission of ACK channel 340.

The ACK channel 340 may use a binary phase shift keying (BPSK)modulation transmitting a positive modulation symbol for a positiveacknowledgment and a negative modulation symbol for a negativeacknowledgment. The ACK/NAK message transmitted on the ACK channel 340may be limited to a single data bit. In a transmitter described inIS-856 standard, the ACK/NAK message passes and repeats through a BPSKmodulator. The BPSK modulator modulates ACK/NAK message, and theresulting signal is Walsh covered in accordance with an assigned Walshcode. In a base station using receiver 400, the ACK channel 340 may bedemodulated. In one embodiment, the signal of the received ACK channel340 may be compared against a positive and negative voltage threshold.If the received signal level meets the positive voltage threshold, anACK message is considered received on the ACK channel 340. If the signallevel meets the negative voltage threshold, a NAK message is consideredreceived on the ACK channel 340.

Referring to FIG. 5, demodulation of ACK channel 340 may be illustrated.The resulting signal may be compared against a positive voltagethreshold 601 and a negative voltage threshold 602. If the signal isabove the positive voltage threshold 601, an ACK message is consideredreceived on the ACK channel 340. If the signal is below the negativevoltage threshold 602, an NAK message is considered received on the ACKchannel 340. The positive and negative voltage thresholds 601 and 602may not be at the same level. As such, an erasure region 603 may becreated between the positive and negative voltage thresholds 601 and602. If the resulting demodulated signal falls in the erasure region603, receiver 400 may not be able to determine whether an ACK or NAKmessage has been transmitted from the mobile station on ACK channel 340.

When the signal is in the erasure region, it is not clear whether an ACKor NAK has been transmitted. If the erasure is changed to an ACK andwhen in fact a NAK is transmitted from the mobile station, the basestation stops transmitting the remainder of the data units, and themobile station would not timely receive the packet of data. One of themeasured system qualities may be the certainty associated with properand on time delivery of a data packet to a mobile station. To avoid sucha problem, in one embodiment, an erasure may be changed to a NAK. If themobile station in fact has transmitted an ACK and receiver 400 in theserving base station detects an erasure, changing the erasure to a NAKmessage presents one or more problems. In such a case, the base stationcontinues the transmission of the remainder data units when in fact thetransmission of the remainder of the data units is not necessary.Unnecessary transmission causes degradation in the system capacity andinterference for other users.

In accordance with various embodiments of the invention in acommunication system 100, a mobile station 102 may be in a soft handoffcondition with base stations 101 and 160. The base station 101 may bethe serving base station on the forward link, and the base station 160may be the non-serving base station on the forward link. Incommunication system 100, a method and accompanying apparatus providefor an efficient acknowledgment of decoding a data packet at servingbase station 101. In accordance with an embodiment, at the serving basestation 101, a message on an acknowledgement channel, such as ACKchannel 340, for indicating the reception of the data packet at mobilestation 102 is received. Receiver 400 at serving base station 101 maydetermine an erasure of the message. In accordance with an embodiment,the non-serving base station 160 may also decode the message on theacknowledgement channel, such as ACK channel 340, from mobile station102. Receiver 400 at the non-serving base station 160 may determine avalue of the message. To determine the value of the message at theserving base station 101 and non-serving base station 160, the receivedsignal of the ACK channel 340 from mobile station 102 may be compared toa modulation voltage threshold, such as thresholds 601 and 602 as shownand described with reference to FIG. 5.

In accordance with an embodiment, the non-serving base station 160 maycommunicate the value of the message to the serving base station 101 viaback-haul 199. The communications over back-haul 199 may be sufficientlyfast for the communication from the non-serving base station 160 to theserving base station 101 to occur in a time less than or equal to a timerequired for the serving base station 101 to schedule a transmission ofthe next data unit in the data units of the data packet. The serving andnon-serving base stations may also determine a reverse link quality fromthe mobile station. The link quality may be measured based on thequality of a pilot channel transmitted from the mobile station.Determining quality of a received pilot channel is well known. In oneaspect, the amplitude and phase of the pilot channel may determine thequality. A higher received amplitude provides a better link quality. Thenon-serving base station may have a better link quality than the servingbase station. In accordance with an embodiment, the serving base station101 may change the erasure of the message to the value of the message asdetermined and communicated by the non-serving base station 160. Thechange may occur when the non-serving base station has a better reverselink quality with the mobile station. The determined value by thenon-serving base station 160 may be a positive acknowledgment of themessage. If the value is a positive acknowledgement, the serving basestation 101 may terminate a transmission of the next data unit of thedata packet to mobile station 102 from the serving base station 101after receiving the positive acknowledgment from the non-serving basestation 160. If the value is a negative acknowledgement, the servingbase station 101 may continue transmission of the remainder data unitsto mobile station 102 from the serving base station 101 after receivingthe negative acknowledgment from the non-serving base station 160.

The mobile station may have an active set of base stations that iscapable of maintaining a communication. The base stations in the activeset have at least a reverse link quality with the mobile station that isadequate for establishing a communication link. The principle ofcreating and maintaining an active set are well known, and described invarious standards incorporated by reference herein. In one embodiment,the non-serving base station may be included in the active set of basestations of the mobile station. The base stations in the active set ofbase stations may demodulate the ACK channel 340 transmitted from themobile station. Each base station in the active set may determinewhether an ACK or NAK is transmitted by the mobile station. The servingbase station may receive the results of demodulating the ACK channel 340at the base stations in the active set. The serving base station maydetermine whether an ACK is transmitted based on the received resultsfrom the active set base stations, when the serving base station detectsan erasure on the ACK channel. If no ACK is detected by any of theactive set base stations, the erasure is considered to be a NAK. If atleast one of the active set base stations with higher quality reverselink detects an ACK, the erasure at the serving base station may bechanged to an ACK, and the transmission of the remaining data units maybe terminated at the serving base station.

Referring to FIG. 6, various aspects of the invention may be moreapparent by referring to flow chart 700. At step 701, a control system,such as control system 410, determines that mobile station 102 is in asoft handoff condition with serving base station 101 and non-servingbase station 160. At step 702, the serving base station 101 receives amessage on an acknowledgement channel for indicating the reception ofthe data packet at the mobile station 102. Receiver 400 at the servingbase station 101 determines an erasure of the message. At step 704, thenon-serving base station 160 may also receives the message on theacknowledgement channel from the mobile station 102. The non-servingbase station 160 determines a value of the message. At step 706, thevalue of the message is communicated from the non-serving base station160 to the serving base station. At step 707, the serving base station101 may change the erasure to the value of the message. At steps 708 and709, if the value of the message is determined to be a positiveacknowledgment message, the serving base station 102 may terminate atransmission of the remainder of data units to the mobile station 102from the serving base station 101 after receiving the positiveacknowledgment from the non-serving base station 160. At steps 710 and711, if the value is a negative acknowledgment message, the serving basestation 101 may schedule transmission of the next data unit in thepacket of data to the mobile station 102 from the serving base station101 after receiving the negative acknowledgement from the non-servingbase station 160. In accordance with an embodiment, the serving andnon-serving base stations may be included in the active set of basestations in the mobile station.

Those of skill in the art would further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination. A softwaremodule may reside in RAM memory, flash memory, ROM memory, EPROM memory,EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or anyother form of storage medium known in the art. An exemplary storagemedium is coupled to the processor such that the processor can readinformation from, and write information to, the storage medium. In thealternative, the storage medium may be integral to the processor. Theprocessor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the presentinvention. The various modifications to these embodiments will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without the use ofthe inventive faculty. Thus, the present invention is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein.

1. A method for receiving data in a wireless communication system,comprising: receiving transmission of a data unit for a packet of datafrom a serving base station; sending, to said serving base station and anon-serving base station, a message on an acknowledgement channel toindicate reception of said packet of data; and receiving transmission ofzero additional data units or an additional data unit for said packet ofdata from said serving base station based on an erasure for said messageat said serving base station and a value of said message sent from saidnon-serving base station to said serving base station.
 2. The method asrecited in claim 1, wherein said receiving transmission of zeroadditional data units or an additional data unit comprises receivingtransmission of zero additional data units for said packet of data fromsaid serving base station based on said erasure at said serving basestation and said value of a positive acknowledgement from saidnon-serving base station.
 3. The method as recited in claim 1, whereinsaid receiving transmission of zero additional data units or anadditional data unit comprises receiving transmission of an additionaldata unit for said packet of data from said serving base station basedon said erasure at said serving base station and said value of anegative acknowledgement from said non-serving base station.
 4. Anapparatus for receiving data in a wireless communication system,comprising: a receiver for receiving transmission of a data unit for apacket of data from a serving base station; and a controller forsending, to said serving base station and a non-serving base station, amessage on an acknowledgement channel to indicate reception of saidpacket of data; and wherein said receiver is further for receivingtransmission of zero additional data units or an additional data unitfor said packet of data from said serving base station based on anerasure for said message at said serving base station and a value ofsaid message sent from said non-serving base station to said servingbase station.
 5. The apparatus as recited in claim 4, wherein saidreceiver is for said receiving transmission of zero additional dataunits for said packet of data from said serving base station based onsaid erasure at said serving base station and said value of a positiveacknowledgement from said non-serving base station.
 6. The apparatus asrecited in claim 4, wherein said receiver is for said receivingtransmission of an additional data unit for said packet of data fromsaid serving base station based on said erasure at said serving basestation and said value of a negative acknowledgement from saidnon-serving base station.
 7. An apparatus for receiving data in awireless communication system, comprising: means for receivingtransmission of a data unit for a packet of data from a serving basestation; means for sending, to said serving base station and anon-serving base station, a message on an acknowledgement channel toindicate reception of said packet of data; and means for receivingtransmission of zero additional data units or an additional data unitfor said packet of data from said serving base station based on anerasure for said message at said serving base station and a value ofsaid message sent from said non-serving base station to said servingbase station.
 8. The apparatus as recited in claim 7, wherein said meansfor receiving transmission of zero additional data units or anadditional data unit comprises means for receiving transmission of zeroadditional data units for said packet of data from said serving basestation based on said erasure at said serving base station and saidvalue of a positive acknowledgement from said non-serving base station.9. The apparatus as recited in claim 7, wherein said means for receivingtransmission of zero additional data units or an additional data unitcomprises means for receiving transmission of an additional data unitfor said packet of data from said serving base station based on saiderasure at said serving base station and said value of a negativeacknowledgement from said non-serving base station.
 10. A non-transitoryprocessor-readable medium including processor-executable instructionsfor performing a method for receiving data in a wireless communicationsystem, the method comprising the steps of: receiving transmission of adata unit for a packet of data from a serving base station; sending, tosaid serving base station and a non-serving base station, a message onan acknowledgement channel to indicate reception of said packet of data;and receiving transmission of zero additional data units or anadditional data unit for said packet of data from said serving basestation based on an erasure for said message at said serving basestation and a value of said message sent from said non-serving basestation to said serving base station.